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2 Tier vs. 3 Tier Storage Pool
Hey everyone,
I was recenlty made aware that the array algorithm used in today's FASTVP seems to work best in a 2-tier vs a 3-tier strategy. Does anyone have anymore insight on this?
Joel
jps00
392 Posts
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June 22nd, 2011 11:00
>the array algorithm used in today's FASTVP seems to work best in a 2-tier vs a 3-tier strategy
Its unclear what you mean by, "seems to work best". After all, its not the difference between a two-wheeler and a tricycle.
There are some advantages to a two-tier pool. For example, with a two-tiered pool using SAS/NL-SAS and FAST Cache, versus a three-tiered pool with Flash/SAS/NL-SAS. That is, the FAST Cache can be used globally for any of the storage system's LUNs, and the Flash drives in the three-tier pool benefit only that pool's LUNs.
jps00
392 Posts
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June 30th, 2011 06:00
Without follow-up, I'm assuming this is answered.
jps00
392 Posts
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June 30th, 2011 07:00
> if i'm not mistaken, a pool that consist of efd will not allow for fast cache.
That is not the case. High usage data in the Flash tier of the pool will be excluded from the FAST Cache. LUN data resident on lower-performing tiers may find its way into the FAST Cache. LUN data already in the FLASH tier will not be promoted into the FAST Cache.
However, you must assume that your highly utilized data will have residence in your Flash tier. That is, LUN data in the lower tiers of a three tiered pool will rarely find its way into a FAST Cache.
HTH.
Addendum: The above is the behavior for O.E. Block 31.0 for VNX, notFLARE 30.X for CLARiiON. My mistake. Primus (emc268101) that says to disable one or the other of tiered Flash drives or FAST Cache for CLARiiON..
odurasler
103 Posts
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June 30th, 2011 07:00
yeah...i'm not sure either.
i was asking guidance on a 3-tier strategy for a particular pool that will consist of efd/fc/sata from someone at emc, and to my surprise, i was told that bit of information. we do have fast cache today and it will be fully populated shortly (~800GB for the cx4-480). if i'm not mistaken, a pool that consist of efd will not allow for fast cache.
so that's why i asked that question because, i'm having to rethink my design.
thanks for your feedback!
odurasler
103 Posts
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July 11th, 2011 17:00
thank you for the clarification!